Nora Valkyrie's Hammer was actually made by the Asgardians where Thor Came from as it was Made Like Storm Breaker and Storm Bringer to give a non-Agardian Thors Powers.

Nora with her Hammer can use it to channel the Powers of thunder similar to Thor Himself as she can summon thunder, fly, and even call her Hammer back to her.

The Hammer was made using A Small piece of Mjolnir Smelted into it similar to the piece that had Given Throg his Powers and it does the same for Nora.

Of course, She named her Hammer Leg Breaker.